1. Field of the Invention
The present invention relates to a document conveying apparatus that can be applied to image forming apparatuses such as copiers and facsimile machines.
2. Description of Related Art
Some image forming apparatuses, such as copiers and facsimile machines, are provided with a document conveying apparatus that automatically feeds a plurality of document sheets to a document reading section. The document conveying apparatus separates and conveys one document sheet after another from the topmost layer of a stack of document sheets stacked on a document stacking tray. The image data on the surface of the document sheets is read by the document reading section, and then the document sheets are ejected into a document ejection tray provided on the downstream end of a document conveying passage.
To feed document sheets from the document stacking tray to the document conveying passage leading to the document reading section, feed members are used such as a feed roller and a feed belt. Such feed members are provided in the downstream portion of the document stacking tray with respect to the document conveying direction, and are pressed onto the topmost layer of the stack of document sheets to feed them to the downstream side with respect to the document conveying direction. Along the document conveying passage, conveying rollers and follower rollers for conveying document sheets are arranged at different positions. A document sheet is passed through nips formed by those conveying rollers and follower rollers pressing against each other, and is thereby conveyed.
In the document conveying apparatus constructed as described above, in the document reading section, the image data on the surface of a document sheet is read by the document reading apparatus as a result of the document sheet coming into contact with or close to the document reading apparatus. Here, inconveniently, the document sheet tends to adhere to a glass portion in the surface of the document reading apparatus. Conventionally, this makes it difficult to separate the document sheet from the glass portion, resulting in lowered conveying performance. To overcome such inconvenience, there has been proposed a construction that facilitates separation of a document sheet from the surface of a document reading apparatus. JP-A-2005-200152 discloses an example of such a construction. In the document feeding apparatus (document conveying apparatus) disclosed in JP-A-2005-200152, a stream of air produced by a fan is blown, from the downstream side with respect to the document conveying direction, onto a platen glass disposed in the reading portion of the document reading apparatus.
The document feeding apparatus (document conveying apparatus) disclosed in JP-A-2005-200152 employs an air stream at the reading portion of the document reading apparatus to facilitate the separation of the document sheet from the platen glass. Thus, from the perspective of preventing the document sheet from adhering to the platen glass, conveying performance is improved. However, the air stream is blown to the document reading apparatus from the downstream side with respect to the document conveying direction, and thus the air stream produces a braking effect on the document sheet. Thus, from the perspective of the very conveying of the document sheet, conveying performance cannot well be said to be improved effectively.
A document sheet may make contact with the conveying rollers, follower rollers, conveying guide members and the like built in the document conveying apparatus, thereby scattering paper powder, toner from the image formed on the document sheet and other particles inside the apparatus. Here, if, as in the document feeding apparatus (document conveying apparatus) disclosed in JP-A-2005-200152, a stream of air is blown from the downstream side with respect to the document conveying direction, the paper powder and toner may fly around inside the apparatus. Thus, the paper powder and toner may adhere to the drive mechanism of the conveying rollers, further lowering the document conveying performance of the apparatus; also the paper powder and toner may adhere to the document reading section, lowering the accuracy with which to read the document sheet. This may greatly affect the quality of the image produced by the image forming apparatus.
On the other hand, there has been proposed, in a document conveying apparatus, separating means that separates, with a stream of air, one document sheet after another from document sheets stacked on a document stacking tray. Here, sheet separation is achieved by blowing a stream of air, from the side of the stack of document sheets, to the downstream-side end face of the stack of document sheets with respect to the document conveying direction and by making float the topmost layer of the stack of document sheets. JP-B-2947855 and JP-A-H09-165144 disclose examples of document conveying apparatuses that in that way facilitate separation of document sheets stacked on top of each other.
Both the automatic document feeding apparatus disclosed in JP-B-2947855 and the automatic document conveying apparatus disclosed in JP-A-H09-165144 blow air to the stack of document sheets stacked on the document stacking tray to facilitate separation of the document sheets as they are fed into the apparatus, thus enhancing paper feed performance. The air stream here is, however, only used to facilitate separating the document sheets as they are fed into the apparatus, and is not used to separate a document sheet from the platen glass or to enhance conveying performance otherwise. Thus, the construction and electric power required to produce the air stream are not used efficiently.
Document conveying apparatuses often incorporate a double-sided document reading apparatus and other components as well as a motor for driving a conveying roller and the control circuit board therefore. An undue rise in temperature due to accumulated heat inside the document conveying apparatus may adversely affect the image formed on the document sheet, the control circuit board and the document reading apparatus, lowering the accuracy with which data is read from the document sheet. Thus, the inside of the document conveying apparatus needs to be cooled efficiently.